川滇高山栎灌丛冠层穿透水及其稳定同位素组成变化特征

植被冠层穿透水有重要的水文学和生态学意义,但目前的工作主要集中在森林植被,缺乏灌丛植被穿透水的报道;而灌丛植被在高山区的水文过程中具有重要作用。为此,在四川卧龙自然保护区3个川滇高山栎灌丛样地收集降水、穿透水和相应的气象资料,测定降水和穿透水的稳定同位素特征,分析各个样地穿透水量和穿透水率的变化,以及穿透水与降水稳定同位素值的差异及变化原因。结果表明穿透水量与降水量呈显著一元线性关系,穿透水率与降水量呈对数正相关。当降水量大于10mm/天时,样地B的穿透水有83.3%出现聚集效应,发生聚集效应时平均穿透水率为114.4%,样地C的穿透水有33.3%发生聚集效应,此时平均穿透水率为104.5%,但样地A没有出现聚集效应,表明在样地A冠层均一程度高。穿透水与降水稳定同位素组成没有显著差异,并有水量效应。但与降水稳定同位素值相比,穿透水稳定同位素值随着穿透水量的增大,先富集重同位素、再贫乏重同位素、最后趋向一致;这与林冠从干燥、蒸发显著,到湿润、出现饱和水汽界面,再到林冠下层形成的水滴占穿透水比重越来越小有关。     

人民币贬值不利于我国外贸企业健康发展──对经济结构改革中我国外贸进出口的分析和预测

本文首先通过对我国出口产品的弹性分析,认为人民币贬值并不能促进我国外贸出口增长,然后对汇率、外贸进出口和经济增长三者之间关系进行研究,认为优化出口产品结构和提高外贸企业自身素质是扩大我国外贸出口的根本途径。最后对下世纪初我国外贸进出口作出展望。     

文献借阅史对采选决策的作用

通过对暨南大学图书馆外文图书2001～2004年外借情况的分析,论述文献借阅史有助于采访人员在宏观上对馆藏文献的学科结构、读者层次结构的把握,在微观上有利于对具体文献的取舍,从而建设具有较高利用率的馆藏。     

How do we rate? An evaluation of online student evaluations

This paper analyses the popular RateMyProfessors (RMP) website where students evaluate instructors in higher education. A study was designed to measure (1) the awareness and utilisation of the RMP website, (2) the internal and external validity of the RMP ratings in measuring teaching effectiveness, and (3) variation in the above across disciplines. It is concluded that the category of ratings, created by the website, establishes an anti‐intellectual tone that manifests itself in comments about instructors’ personality, easiness of workload and entertainment value rather than knowledge attained.     

Educational Attainment as Process: Using Hierarchical Discrete-Time Event History Analysis to Model Rate of Progress

Variables that address student enrollment patterns (e.g., persistence, enrollment inconsistency, completed credit hours, course credit load, course completion rate, procrastination) constitute a longstanding fixture of analytical strategies in educational research, particularly research that focuses on explaining variation in academic outcomes. However, nearly all measures of enrollment patterns are handicapped by untested assumptions about a more fundamental measure, namely students’ rate of progress. In this paper, I first explain how a variety of widely used measures of enrollment patterns are inextricably linked to students’ rate of progress. I then describe a method of modeling mathematically students’ rate of progress that employs hierarchical (multilevel) discrete-time event history analysis of repeated events. I conclude with an empirical example of the application of this method in which I test several hypotheses concerning students’ rate of progress through the remedial math sequence toward the outcome of college-level math competency. In addition to the utility of the method that is proposed here, the issues discussed in this paper have important practical implications for institutional research, particularly with respect to the use of the various measures of enrollment patterns to explain variation in students’ attainment.

复杂网络统计参量对病毒传播速率的影响

复杂网络统计参量是描述复杂网络结构的普适参量,病毒的传播与这些基本参量密切相关,病毒传播速率与复杂网络统计参量间存在确定的联系。文章推论了复杂网络中病毒传播速率与基本网络参量的函数关系。利用这一函数可以在已知的网络结构参数时,得到病毒传播的预测值。     

Stress reactivity after maximal exercise: The effect of manipulated performance feedback in endurance athletes

This study was designed to assess the effect of performance feedback on stress reactivity after recovery from maximal exercise. Forty competitive athletes were recruited to complete a maximal exercise test. Performance feedback was manipulated after the exercise test to give four groups: (1) high performance, (2) low performance, (3) accurate feedback and (4) no exercise control. Cardiovascular reactivity was assessed during psychological stress. The results indicate that accurate feedback participants experienced lower relative reactivity to stress (lower mean arterial pressure) than their no-exercise counterparts. These results demonstrate that the stressbuffering effect of exercise extends to maximal exercise. In addition, high-performance participants experienced lower relative reactivity than low-performance participants. Thus, low-performance feedback was sufficient to remove the buffering effect of exercise. There were no differences between the high-performance and accurate feedback conditions, or between the low-performance and control conditions.     

Physiological demands of top-class soccer refereeing in relation to physical capacity: effect of intense intermittent exercise training

To examine the activity profile and physiological demands of top-class soccer refereeing, we performed computerized time-motion analyses and measured the heart rate and blood lactate concentration of 27 referees during 43 competitive matches in the two top Danish leagues. To relate match performance to physical capacity and training, several physiological tests were performed before and after intermittent exercise training. Total distance covered was 10.07 - 0.13 km (mean - s x ), of which 1.67 - 0.08 km was high-intensity running. High-intensity running and backwards running decreased (P ? 0.05) in the second half. Mean heart rate was 162 - 2 beats· min -1 (85 - 1% of maximal heart rate) and the mean blood lactate concentration was 4.9 - 0.3 (range 1.7-14.0) mmol·l -1 . The amount of high-intensity running during a match was related to the Yo-Yo intermittent recovery test ( r 2 = 0.57; P ? 0.05) and the 12 min run ( r 2 = 0.21; P ? 0.05). After intermittent training ( n = 8), distance covered during high-intensity running was greater (2.06 - 0.13 vs 1.69 - 0.08 km; P ? 0.05) and mean heart rate was lower (159 - 1 vs 164 - 2 beats· min -1 ; P ? 0.05) than before training. The results of the present study demonstrate that: (1) top-class soccer referees have significant aerobic energy expenditure throughout a game and episodes of considerable anaerobic energy turnover; (2) the ability to perform high-intensity running is reduced towards the end of matches; (3) the Yo-Yo intermittent recovery test can be used to evaluate referees' match performance; and (4) intense intermittent exercise training improves referees' performance capacity during a game.     

山东省科技进步贡献率的测算及对策研究

本文基于柯布-道格拉斯函数和索洛余值法,测算了山东省从1990年到2011年间科技进步在经济增长中的作用;通过测算得到的结果,提出了山东省在今后科技发展中的相关对策。     

对人民币汇率安排的几点思考

本文从人民币升值的国内外背景、人民币币值稳定的宏观经济意义、人民币升值的利弊及影响人民币汇率变动的因素着手分析，得出在近期内人民币汇率仍应保持稳定。文章进一步提出了考虑到中国未来经济发展的趋势，为保持人民币币值稳定，应适时调整汇率制度，以化解目前的升值压力，提高汇率政策的作用，并提出了相关建议。